i do not recommend dividing by cos^2 x. if a solution of x ends up being one that causes cos(x) = 0, it would mean you have divided by 0, hence making your solution invalid. bring everything to one side and factor out the cos^2 x instead

68. How do you simplify/factorise this?

no factorization necessary, just solve for sin^4 x and take it from there

So cos^2x isn't common through out the equation and so cannot take out as a factor?

you could have taken out cos^2 x out of the terms where it's common. but i made a post saying why it is ok to divide by cos^2 x, so don't worry about it

EDIT: i'm kind of busy with other stuff right now, and as a result, i cannot concentrate on your problems as much as i would like to. i'm going to log off. hopefully someone else will help you. if not, i'll pick up where i left off when i come back on again